Estimating phase using test phases and interpolation for modulation formats using multiple sub-carriers

ABSTRACT

An optical receiver may receive input signals carried by sub-carriers, and may apply test phases to each input signal. The optical receiver may determine error values, associated with test phases, for each input signal. The optical receiver may calculate updated metric values, associated with the test phases, for a particular input signal, based on a first error value and a second error value. The first error value may be associated with a first sub-carrier, and the second error value may be associated with a second sub-carrier. The optical receiver may compare the updated metric values associated with the particular input signal, and may determine a test phase that represents an estimated phase, associated with the particular input signal, based on the comparison. The optical receiver may determine a phase estimate value based on the test phase, and may provide the phase estimate value to modify the particular input signal.

BACKGROUND

Wavelength division multiplexed (WDM) optical communication systems(referred to as “WDM systems”) are systems in which multiple opticalsignals, each having a different wavelength, are combined onto a singleoptical fiber using an optical multiplexer circuit (referred to as a“multiplexer”). Such systems may include a transmitter circuit, such asa transmitter (Tx) photonic integrated circuit (PIC) having atransmitter component to provide a laser associated with eachwavelength, a modulator configured to modulate the output of the laser,and a multiplexer to combine each of the modulated outputs (e.g., toform a combined output or WDM signal).

A WDM system may also include a receiver circuit having a receiver (Rx)PIC and an optical demultiplexer circuit (referred to as a“demultiplexer”) configured to receive the combined output anddemultiplex the combined output into individual optical signals.Additionally, the receiver circuit may include receiver components toconvert the optical signals into electrical signals, and output the datacarried by those electrical signals.

SUMMARY

According to some possible implementations, an optical receiver mayinclude a digital signal processor. The digital signal processor mayreceive input signals carried by respective sub-carriers. The digitalsignal processor may apply test phases to each input signal, and maydetermine error values, respectively associated with the test phases,for each input signal. The digital signal processor may selectivelycombine a first error value, associated with a first input signal, and asecond error value, associated with a second input signal. The firstinput signal may be carried by a first sub-carrier, and the second inputsignal may be carried by a second sub-carrier. The second sub-carriermay be different from the first sub-carrier. The digital signalprocessor may calculate updated metric values, respectively associatedwith the test phases, for a particular input signal, based onselectively combining the first error value and the second error value.The digital signal processor may compare the updated metric valuesassociated with the particular input signal, and may determine a testphase that represents an estimated phase, associated with the particularinput signal, based on comparing the plurality of updated metric values.The digital signal processor may determine a phase estimate value basedon the test phase, and may provide the phase estimate value to modifythe particular input signal.

According to some possible implementations, a system may include anoptical receiver. The optical receiver may receive input signals carriedby respective sub-carriers, and may apply test phases to each inputsignal. The optical receiver may determine error values, respectivelyassociated with test phases, for each input signal. The optical receivermay calculate updated metric values, respectively associated with thetest phases, for a particular input signal, based on a first error valueand a second error value. The first error value may be associated with afirst sub-carrier, and the second error value may be associated with asecond sub-carrier. The second sub-carrier may be different from thefirst sub-carrier. The optical receiver may compare the updated metricvalues associated with the particular input signal, and may determine atest phase that represents an estimated phase, associated with theparticular input signal, based on comparing the updated metric values.The optical receiver may determine a phase estimate value based on thetest phase, and may provide the phase estimate value to modify theparticular input signal.

According to some possible implementations, a method may includereceiving, by an optical receiver, input signals carried by respectivesub-carriers. The method may include applying, by the optical receiver,test phases to each input signal, and determining, by the opticalreceiver, error values, respectively associated with test phases, foreach input signal. The method may include calculating, by the opticalreceiver, final error values, respectively associated with the testphases, for a particular input signal, based on a first error value anda second error value. The first error value may be associated with afirst sub-carrier, and the second error value may be associated with asecond sub-carrier. The second sub-carrier may be different from thefirst sub-carrier. The method may include comparing, by the opticalreceiver, the final error values, associated with the particular inputsignal, to determine a minimum final error value. The method may includeidentifying, by the optical receiver, a test phase associated with theminimum final error value, and determining, by the optical receiver andbased on the identified test phase, a phase estimate value thatrepresents an estimated phase associated with the particular inputsignal. The method may include providing, by the optical receiver, thephase estimate value to modify the particular input signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are diagrams of an overview of an example implementationdescribed herein;

FIG. 2 is a diagram of an example network in which systems and/ormethods, described herein, may be implemented;

FIG. 3 is a diagram of example components of an optical transmittershown in FIG. 2;

FIG. 4 is a diagram of example components of an optical receiver shownin FIG. 2;

FIGS. 5A and 5B are diagrams of example components of a carrier recoverycomponent shown in FIG. 4; and

FIGS. 6-8, 9A, 9B, 10-12, and 13A-13D are diagrams of exampleimplementations relating to operations performed by components of thecarrier recovery component shown in FIGS. 5A and 5B.

DETAILED DESCRIPTION

The following detailed description of example implementations refers tothe accompanying drawings. The same reference numbers in differentdrawings may identify the same or similar elements.

In a WDM system, a transmitter may modulate an amplitude and/or a phaseof a signal in order to convey data, via the signal, to a receiver wherethe signal may be demodulated to recover the data included in thesignal. A particular modulation format (e.g., phase-shift keying (PSK),quadrature amplitude modulation (QAM), quadrature phase-shift keying(QPSK), binary phase-shift keying (BPSK), polarization-multiplexedquadrature phase-shift keying (PM-QPSK), etc.) may be used to modulatethe signal. When the signal is transmitted or received over a link,random phase fluctuations in the signal may be introduced via thetransmitter, the receiver, and/or the link. These random phasefluctuations may be compensated by the receiver during carrier phaserecovery to correct a phase error introduced into the modulated signal,thus permitting the receiver to properly decode the modulated signal.

In a coherent receiver, the received signal is sampled byanalog-to-digital converters (ADCs) for signal processing. Although 2samples/symbol or less may be used for the CD compensation and PMDequalization, the subsequent carrier recovery uses 1 sample/symbol.During carrier phase recovery, the receiver may apply test phases to areceived sample to determine the most-likely transmitted symbol. Forexample, the receiver may apply a maximum likelihood phase estimatetechnique by rotating a received sample using each test phase to decodethe received sample into a symbol. The receiver may determine whichrotated sample is closest to (e.g., has the smallest Euclidean distanceto) a constellation point (e.g., included in a constellation diagram fora particular modulation format), which corresponds to the decodedsymbol. However, this technique may require a large number of testphases to generate an accurate estimate of the phase to be corrected forthe received sample, which may be computationally expensive.Implementations described herein reduce the computational complexity ofaccurately estimating the phase error contained in a received sample.Furthermore, implementations described herein introduce a technique forperforming carrier recovery when signals are transmitted using multipledigital sub-carriers, rather than a single carrier.

FIGS. 1A-1C are diagrams of an overview of an example implementation 100described herein. FIG. 1A shows a constellation diagram that representsall possible symbols that may be transmitted via a signal modulatedusing a rectangular 16QAM modulation format. As shown by referencenumber 105, some of the constellation points (e.g., symbols) in theconstellation diagram are separated by a phase difference of 90 degrees(e.g., the constellation points represented by a white dot with a blackoutline). As shown by reference number 110, when a receiver receives asample corresponding to a symbol, the sample may include a phase errorthat, if not corrected, would be decoded to an incorrect symbol in theconstellation diagram. For example, a phase error may have beenintroduced into the sample during transmission (e.g., due to randomnoise introduced into the sample/signal by the receiver, by atransmitter, during transmission via a fiber, etc.). The receiver maycorrect a phase error in the sample by rotating the sample using a setof test phases, and determining an error (e.g., a distance), for eachtest phase, between the rotated sample and the nearest constellationpoint in the constellation diagram. For example, the receiver may rotatethe received sample using a set of test phases between −45 degrees and45 degrees, as shown. As shown by reference number 115, applying thiscarrier recovery technique to a constellation point with a 90 degreephase difference results in one minimum error value, which correspondsto the phase estimate for carrier recovery.

This carrier recovery technique cannot be used to easily correct a phaseerror associated with symbols in the constellation diagram that areseparated by a phase difference of 36.87 degrees or 53.13 degrees (e.g.,the symbols represented by a black dot with a black outline), which areshown by reference number 120. The star in the constellation diagramrepresents a received sample. As shown, the receiver may scan +/−45degrees from the received sample to identify a correct constellationpoint. Assume that the correct constellation point is found at a testphase of zero degrees, which corresponds to a first minimum error value.However, there is also a second minimum error value at a test phase of−36.87 degrees, which causes an ambiguity. These two minima associatedwith the error values (e.g., at 0 degrees and −36.87 degrees) are alsoshown by reference number 125.

As shown in FIG. 1B, and by reference number 130, assume that theminimum error value for the received 90 degree phase difference symbolcorresponds to a phase rotation of 20 degrees. Thus, to perform carrierrecovery for the received sample, the receiver may rotate the phase ofthe received sample by 20 degrees to correct for the phase error so thatthe received sample may be properly decoded to the transmitted symbol,as shown by reference number 135.

As shown by reference number 140, assume that the two minimum errorvalues for correspond to test phases of zero degrees and −36.87 degrees.Assume that the receiver properly performs carrier recovery by selectingthe test phase of zero degrees. To perform carrier recovery foradditional received samples, the receiver may use test phases that rangefrom −22.5 degrees and 22.5 degrees around the selected test phase(e.g., a 45 degree sweep centered at 0 degrees), thereby eliminating thepossibility of determining two minimum error values, as shown byreference number 150. Thus, implementations described herein assist inaccurately and efficiently correcting phase errors in received samples.

As shown in FIG. 1C, implementations described herein may also assist inaccurately and efficiently correcting phase errors in received sampleswhen the samples are carried on signals transmitted via multiple digitalsub-carriers. Note that by using digital subcarriers, the transmitterand the receiver may use one laser centered at the center of the overallsignal spectrum. In an optical communication system, a certainbandwidth, or spectrum, may be allocated to an optical communicationschannel. As shown by reference number 155, the channel may include asingle carrier that carries data via the optical channel. In this case,implementations described herein may use a phase estimate of the singlecarrier for carrier recovery. As shown by reference number 160, ratherthan including a single carrier, the channel may include multiplesub-carriers that carry data via the optical channel. In this case,implementations described herein may use an average phase estimate ofmultiple sub-carriers for carrier recovery. In this way, the receivermay accurately and efficiently determine phase estimates for receivedsymbols, resulting in more accurate and efficient data transmission.

Implementations described herein may perform carrier recovery fordifferent modulation formats, such as M-QAM modulation formats (e.g.,3QAM, 5QAM, 7QAM, 8QAM, 16QAM, etc.), BPSK modulation formats (e.g.,Block-4D-BPSK, etc.), QPSK modulation formats (e.g., PM-QPSK, etc.), orthe like.

FIG. 2 is a diagram of an example network 200 in which systems and/ormethods, described herein, may be implemented. As shown in FIG. 2,network 200 may include transmitter (Tx) module 210 (e.g., a Tx PIC),and/or receiver (Rx) module 220 (e.g., an Rx PIC). In someimplementations, transmitter module 210 may be optically connected toreceiver module 220 via link 230. Additionally, link 230 may include oneor more optical amplifiers 240 that amplify an optical signal as theoptical signal is transmitted over link 230.

Transmitter module 210 may include one or more optical transmitters212-1 through 212-M (M≧1), one or more waveguides 214, and/or an opticalmultiplexer 216. In some implementations, transmitter module 210 mayinclude additional components, fewer components, different components,or differently arranged components than those shown in FIG. 2.

Optical transmitter 212 may receive data for a data channel (shown asTxCh1 through TxChM), may create multiple sub-carriers for the datachannel, may map data, for the data channel, to the multiplesub-carriers, may modulate the data with an optical signal (e.g., alaser) to create a multiple sub-carrier output optical signal, and maytransmit the multiple sub-carrier output optical signal. Opticaltransmitter 212 may be tuned to use an optical carrier of a designatedwavelength. In some implementations, the grid of wavelengths emitted byoptical transmitters 212 may conform to a known standard, such as astandard published by the Telecommunication Standardization Sector(ITU-T). Additionally, or alternatively the grid of wavelengths may beflexible and tightly packed to create a super channel.

Waveguide 214 may include an optical link or some other link to transmitoutput optical signals of optical transmitter 212. In someimplementations, each optical transmitter 212 may include one waveguide214, or multiple waveguides 214, to transmit output optical signals ofoptical transmitters 212 to optical multiplexer 216.

Optical multiplexer 216 may include an arrayed waveguide grating (AWG)or some other type of multiplexer device. In some implementations,optical multiplexer 216 may combine multiple output optical signals,associated with optical transmitters 212, into a single optical signal(e.g., a WDM signal). For example, optical multiplexer 216 may includean input (e.g., a first slab to receive input optical signals suppliedby optical transmitters 212) and an output (e.g., a second slab tosupply a single WDM signal associated with the input optical signals).Additionally, optical multiplexer 216 may include waveguides connectedto the input and the output. In some implementations, opticalmultiplexer 216 may combine multiple output optical signals, associatedwith optical transmitters 212, in such a way as to produce apolarization diverse signal (e.g., also referred to herein as a WDMsignal). As shown in FIG. 2, optical multiplexer 216 may provide the WDMsignal to receiver module 220 via an optical fiber, such as link 230.

Optical multiplexer 216 may receive output optical signals outputted byoptical transmitters 212, and may output one or more WDM signals. EachWDM signal may include one or more optical signals, such that eachoptical signal includes one or more wavelengths. In someimplementations, one WDM signal may have a first polarization (e.g., atransverse magnetic (TM) polarization), and another WDM signal may havea second, substantially orthogonal polarization (e.g., a transverseelectric (TE) polarization). Alternatively, both WDM signals may havethe same polarization.

Link 230 may include an optical fiber. Link 230 may transport one ormore optical signals associated with multiple wavelengths. Amplifier 240may include an amplification device, such as a doped fiber amplifier, aRaman amplifier, or the like. Amplifier 240 may amplify the opticalsignals as the optical signals are transmitted via link 230.

Receiver module 220 may include an optical demultiplexer 222, one ormore waveguides 224, and/or one or more optical receivers 226-1 through226-N(N≧1). In some implementations, receiver module 220 may includeadditional components, fewer components, different components, ordifferently arranged components than those shown in FIG. 2.

Optical demultiplexer 222 may include an AWG or some other type ofdemultiplexer device. In some implementations, optical demultiplexer 222may supply multiple optical signals based on receiving one or moreoptical signals, such as WDM signals, or components associated with theone or more optical signals. For example, optical demultiplexer 222 mayinclude an input (e.g., a first slab to receive a WDM signal and/or someother input signal), and an output (e.g., a second slab to supplymultiple optical signals associated with the WDM signal). Additionally,optical demultiplexer 222 may include waveguides connected to the inputand the output. As shown in FIG. 2, optical demultiplexer 222 may supplyoptical signals to optical receivers 226 via waveguides 224.

Waveguide 224 may include an optical link or some other link to transmitoptical signals, output from optical demultiplexer 222, to opticalreceivers 226. In some implementations, each optical receiver 226 mayreceive optical signals via a single waveguide 224 or via multiplewaveguides 224.

Optical receiver 226 may include one or more photodetectors and/orsimilar devices to receive respective input optical signals outputted byoptical demultiplexer 222, to detect sub-carriers associated with theinput optical signals, to convert data within the sub-carriers tovoltage signals, to convert the voltage signals to digital samples, andto process the digital samples to produce output data corresponding tothe input optical signals. Optical receivers 226 may each operate toconvert the input optical signal to an electrical signal that representsthe transmitted data.

The number and arrangement of components shown in FIG. 2 is provided asan example. In practice, network 200 may include additional components,fewer components, different components, or differently arrangedcomponents than those shown in FIG. 2. Additionally, or alternatively, aset of devices (e.g., one or more devices) shown in FIG. 2 may performone or more functions described herein as being performed by another setof devices shown in FIG. 2.

FIG. 3 is a diagram of example components of an optical transmitter 212.As shown in FIG. 3, optical transmitter 212 may include a TX DSP 310,one or more DACs 320, a laser 330, and one or more modulators 340. Insome implementations, TX DSP 310, DAC 320, laser 330, and/or modulator340 may be implemented on one or more integrated circuits, such as oneor more PICs, one or more application specific integrated circuits(ASICs), or the like. In some implementations, components of multipleoptical transmitters 212 may be implemented on a single integratedcircuit, such as a single PIC, to form a super-channel transmitter.

TX DSP 310 may include a digital signal processor. TX DSP 310 mayreceive input data from a data source, and may determine a signal toapply to modulator 340 to generate multiple sub-carriers. In someimplementations, TX DSP 310 may receive streams of data, may map thestreams of data onto each of the sub-carriers, may independently applyspectral shaping to each of the sub-carriers, and may obtain, based onthe spectral shaping of each of the sub-carriers, a sequence of assignedintegers to supply to DAC 320. In some implementations, TX DSP 310 maygenerate the sub-carriers using time-domain or frequency-domainfiltering and frequency shifting by a combination of reallocation offrequency bins and multiplication in the time domain.

DAC 320 may include a signal converting device or a collection of signalconverting devices. In some implementations, DAC 320 may receiverespective digital signals from TX DSP 310, may convert the receiveddigital signals to analog signals, and may provide the analog signals tomodulator 340. The analog signals may correspond to electrical signals(e.g., voltage signals) to drive modulator 340. In some implementations,transmitter module 212 may include multiple DACs 320, where a particularDAC 320 may correspond to a particular in-phase (I) or quadraturecomponent (Q) of a particular polarization (e.g., an X polarization, a Ypolarization) of a dual-pol signal.

Laser 330 may include a semiconductor laser, such as a distributedfeedback (DFB) laser, or some other type of laser. Laser 330 may providean output optical light beam to modulator 340.

Modulator 340 may include a Mach-Zehnder modulator (MZM), such as anested MZM, or another type of modulator. Modulator 340 may receive theoptical light beam from laser 330 and the voltage signals from DAC 320,and may modulate the optical light beam, based on the voltage signals,to generate a multiple digital sub-carrier output signal, which may beprovided to multiplexer 216.

In some implementations, optical transmitter 212 may include multiplemodulators 340, which may be used to modulate signals of differentpolarizations. For example, an optical splitter may receive an opticallight beam from laser 330, and may split the optical light beam into twobranches: one for a first polarization and one for a secondpolarization. The splitter may output one optical light beam to a firstmodulator 340, which may be used to modulate signals of the firstpolarization, and another optical light beam to a second modulator 340,which may be used to modulate signals of the second polarization. Insome implementations, two DACs 320 may be associated with eachpolarization. In these implementations, two DACs 320 may supply voltagesignals to the first modulator 340 (e.g., for an in-phase component ofan X polarization and a quadrature component of the X polarization), andtwo DACs 320 may supply voltage signals to the second modulator 340(e.g., for an in-phase component of a Y polarization and a quadraturecomponent of the Y polarization). The outputs of modulators 340 may becombined back together using combiners (e.g., optical multiplexer 216)and polarization multiplexing.

The number and arrangement of components shown in FIG. 3 is provided asan example. In practice, optical transmitter 212 may include additionalcomponents, fewer components, different components, or differentlyarranged components than those shown in FIG. 3. For example, thequantity of DACs 320, lasers 330, and/or modulators 340 may be selectedto implement an optical transmitter 212 that is capable of generatingpolarization diverse signals for transmission on an optical fiber, suchas link 230. Additionally, or alternatively, a set of components shownin FIG. 3 may perform one or more functions described herein as beingperformed by another set of components shown in FIG. 3.

FIG. 4 is a diagram of example components of optical receiver 226. Asshown in FIG. 4, optical receiver 226 may include a local oscillator410, one or more hybrid mixers 420, one or more detectors 430, one ormore ADCs 440, and an RX DSP 450, which may include a carrier recoverycomponent (CRC) 460. In some implementations, local oscillator 410,hybrid mixer 420, detector 430, ADC 440, and/or RX DSP 450 may beimplemented on one or more integrated circuits, such as one or morePICs, one or more ASICs, or the like. In some implementations,components of multiple optical receivers 226 may be implemented on asingle integrated circuit, such as a single PIC plus one or more ASICs,to form a super-channel receiver.

Local oscillator 410 may include a laser, or a similar device. In someimplementations, local oscillator 410 may include a laser to provide anoptical signal to hybrid mixer 420. In some implementations, localoscillator 410 may include a single-sided laser to provide an opticalsignal to hybrid mixer 420. In some implementations, local oscillator410 may include a double-sided laser to provide multiple optical signalsto multiple hybrid mixers 420.

Hybrid mixer 420 may include a combiner that receives a first opticalsignal (e.g., an input signal from optical demultiplexer 222) and asecond optical signal (e.g., from local oscillator 410) and combines thefirst and second optical signals to generate a combined optical signal.In some implementations, hybrid mixer 420 may include a polarizationbeam splitter (PBS) which splits the first optical signal into twoorthogonal signals. The two orthogonal signals may be combined withrespective second optical signals (from a laser) with 90 degree phasewith respect to each other. Hybrid mixer 420 may provide the combinedoptical signal to detector 430.

Detector 430 may include a photodetector, such as a photodiode, toreceive the output optical signal, from hybrid mixer 420, and to convertthe output optical signal to corresponding voltage signals. In someimplementations, detector 430 may detect the entire spectrum of theoutput optical signal (e.g., containing all of the sub-carriers).

In some implementations, optical receiver 226 may include multipledetectors 430, which may be used to detect signals of respective I and Qcomponents of the two orthogonal polarizations. For example, apolarization splitter may receive an input signal, and may split theinput signal into two substantially orthogonal polarizations, such asthe first polarization and the second polarization. Hybrid mixers 420may combine the polarization signals with optical signals from localoscillator 410. For example, a first hybrid mixer 420 may combine afirst polarization signal with the optical signal from local oscillator410, and a second hybrid mixer 420 may combine a second polarizationsignal with the optical signal from local oscillator 410 with 90 degreephase with respect to the first signal of the local oscillator.

Detectors 430 may detect the polarization signals to form correspondingvoltage signals, and ADCs 440 may convert the voltage signals to digitalsamples. For example, two detectors 430 (e.g., balanced PIN diodes) maydetect the first polarization signals to form the corresponding voltagesignals, and a corresponding two ADCs 440 (e.g., that correspond to an Icomponent and a Q component) may convert the voltage signals to digitalsamples for the first polarization signals. Similarly, two detectors 430may detect the second polarization signals to form the correspondingvoltage signals, and a corresponding two ADCs 440 (e.g., that correspondto an I component and a Q component) may convert the voltage signals todigital samples for the second polarization signals. RX DSP 450 mayprocess the digital samples for the first and second polarizationsignals to generate resultant data, which may be outputted as outputdata.

ADC 440 may include four analog-to-digital converters that convert thevoltage signals from detector 430 to digital samples. ADC 440 mayprovide the digital samples to RX DSP 450.

RX DSP 450 may include a digital signal processor. RX DSP 450 mayreceive the digital samples from ADC 440, may demultiplex the samplesaccording to the subcarriers, may independently process the samples foreach of the subcarriers, may map the processed samples to produce outputdata, and may output the output data. RX DSP 450 may include CRC 460,which may include one or more components for performing carrierrecovery, as described in more detail elsewhere herein.

The number and arrangement of components shown in FIG. 4 is provided asan example. In practice, optical receiver 226 may include additionalcomponents, fewer components, different components, or differentlyarranged components than those shown in FIG. 4. For example, thequantity of hybrid mixers 420, detectors 430, and/or ADCs 440 may beselected to implement an optical receiver 226 that is capable ofreceiving and processing a polarization diverse signal. Additionally, oralternatively, a set of components shown in FIG. 4 may perform one ormore functions described herein as being performed by another set ofcomponents shown in FIG. 4.

FIGS. 5A and 5B are diagrams of example components of carrier recoverycomponent 460 shown in FIG. 4. As shown in FIG. 5A, carrier recoverycomponent 460 may include a first-in first-out delay component (FIFODelay) 505, a multiplier component 510, a frequency and phasecompensation component (FAPC) 515, a phase test component 520, a metricfiltering component 525, a phase estimate component 530, a phase unwrapcomponent 535, another FIFO Delay component 540, an adder component 545,a lookup table component (LUT) 550, a frequency estimate component 555,and a phase difference estimate component 560.

Carrier recovery component (CRC) 460 may receive an input signal (e.g.from the output of an equalizer), and may pass the input signal to FIFODelay 505, which may delay the input signal to compensate for delayintroduced by operations performed by other components of CRC 460 (e.g.,components 515-550) prior to an adjustment signal being received bymultiplier component 510. Multiplier component 510 may receive the inputsignal from FIFO Delay 505, and may adjust the input signal (e.g., viamultiplication, rotation, etc.) using an adjustment signal received fromLUT 550. For example, multiplier component 510 may adjust a phase of theinput signal using an output phase value received from LUT 550.Multiplier component 510 may output the adjusted signal as an outputsignal from CRC 460, and may further output the adjusted signal to afeedback loop that includes phase difference estimate component 560.

CRC 460 may also pass the input signal to FAPC 515. Components 515-550may operate on the input signal to determine the output phase value tobe provided to multiplier 510. Components 555 and 560 may be included ina feedback loop that determines feedback signals to be used to adjustoperations of components 515-550 (e.g., FAPC 515).

As shown in FIG. 5B, FAPC 515 may provide a phase and/or frequencycompensated signal to phase test component 520. Phase test component 520may apply test phases to the signal, and may determine error valuesbased on applying the test phases. Metric filtering component 525 mayreceive the error values, and may average the error values over timeand/or over multiple sub-carriers. Phase estimate component 530 mayreceive the averaged error values, and may determine one or more phaseestimates for the input signals based on the averaged error values.Phase unwrap component 535 may unwrap the phase estimate values across afull phase cycle (e.g., 360 degrees), and may provide the unwrappedphase estimate as shown in FIG. 5A. Components of CRC 460 will bedescribed in more detail elsewhere herein.

The number of components shown in FIGS. 5A and 5B is provided as anexample. In practice, CRC 460 may include additional components, fewercomponents, different components, or differently arranged componentsthan those shown in FIGS. 5A and 5B. Additionally, or alternatively, aset of components of CRC 460 may perform one or more functions describedas being performed by another set of components of CRC 460.

FIG. 6 is a diagram of an example implementation 600 relating tooperations performed by frequency and phase compensation component(FAPC) 515. As shown in FIG. 6, FAPC 515 may receive an input signal(e.g., a digital sample, a digital signal, etc.). In exampleimplementation 600, FAPC 515 is shown as receiving 16 samples, on eachof 4 sub-carriers that each have two polarizations (e.g., Xpol andYpol), per clock cycle. Thus, FAPC 515 receives 64 samples on the Xpolarization (e.g., 16 samples×4 sub-carriers carrying data on the Xpolarization) and 64 samples on the Y polarization (e.g., 16 samples×4sub-carriers carrying data on the Y polarization), for a total of 128samples per clock cycle. Each sample may include a symbol (e.g., with aphase value and an amplitude value).

In some implementations, FAPC 515 may compensate the frequency of theinput signal(s) using a frequency estimate value (FreqEstVal) receivedfrom frequency estimate component (FE) 555, determined as describedelsewhere herein.

Additionally, or alternatively, FAPC 515 may compensate a phasedifference between the X polarization and the Y polarization for eachsub-carrier using a first phase difference value (phiDiff_(—)1, or(Φ_(diff1)) received from PDE 560, determined as described elsewhereherein. In some implementations, the quantity of phiDiff_(—)1 valuesreceived from PDE 560 may correspond to the quantity of sub-carriers.For example, PDE 560 is shown as providing four phiDiff_(—)1 values toFAPC 515 (e.g., phiDiff_(—)1[0], phiDiff_(—)1[1], phiDiff_(—)1[2], andphiDiff_(—)1[3]), where the values of 0-3 correspond to the 4sub-carriers of example implementation 600.

Additionally, or alternatively, FAPC 515 may compensate a phasedifference between different sub-carriers using a second phasedifference value (phiDiff_(—)2, or Φ_(diff2)) received from PDE 560,determined as described elsewhere herein. In some implementations, thequantity of phiDiff_(—)2 values received from PDE 560 may correspond tothe quantity of sub-carriers. For example, PDE 560 is shown as providingfour phiDiff_(—)2 values to FAPC 515 (e.g., phiDiff_(—)2[0],phiDiff_(—)2[1], phiDiff_(—)2[2], and phiDiff_(—)2[3]), where the valuesof 0-3 correspond to the 4 sub-carriers of example implementation 600.

For each sub-carrier s, FAPC 515 may compensate a sample received viathe sub-carrier, based on input received from FE 555 and PDE 560, asfollows:

x′ _(s) [n]=x _(s) [n]×e ^(−j[XCompvalue) ^(s) ^([n]])

y′ _(s) [n]=y _(s) [n]×e ^(−j[YCompvalue) ^(s) ^([n]])

In the above equations, x′_(s) [n] and y′_(s) [n] may represent thefrequency and phase compensated symbols, for the n^(th) sample (or attime n) of sub-carrier s, calculated by FAPC 515 for the X polarizationand the Y polarization, respectively. Furthermore, x_(s) [n] and y_(s)[n] may represent the input symbols before adjustment, e may representEuler's number (e.g., the mathematical constant e≈2.71828), j mayrepresent the imaginary component of the sample (e.g., the square rootof −1), and XCompValue_(s)[n] and YCompValue_(s)[n] may represent Xpolarization and Y polarization compensation values, respectively, to beapplied to the input symbols by FAPC 515. In some implementations,XCompValue_(s)[n] and YCompValue_(s)[n] may be represented as follows:

${{XCompValue}_{s}\lbrack n\rbrack} = {\left( {\int_{- \infty}^{n}{FreqEstVal}} \right) + \frac{\varphi_{{diff}\; 1}\lbrack s\rbrack}{2} + {\varphi_{{diff}\; 2}\lbrack s\rbrack}}$${{YCompValue}_{s}\lbrack n\rbrack} = {\left( {\int_{- \infty}^{n}{FreqEstVal}} \right) - \frac{\varphi_{{diff}\; 1}\lbrack s\rbrack}{2} + {\varphi_{{diff}\; 2}\lbrack s\rbrack}}$

In the above equations, FreqEstVal may represent the frequency estimatevalue received from FE 555, Φ_(diff1) may represent the first phasedifference value received from PDE 560, and Φ_(diff2) may represent thesecond phase difference value received from PDE 560. As used herein, afrequency compensation value may refer to the frequency estimate value(FreqEstVal), an integral of the frequency estimate value (e.g., fromn_(initial) to n_(final), such as from negative infinity to n), or thelike. As used herein, a phase compensation value may refer to the firstphase difference value (e.g., Φ_(diff1)), the second phase differencevalue (e.g., Φ_(Diff2)), a mathematical combination of the first phasedifference value and the second phase difference value (e.g.,

$\left. {\frac{\varphi_{{diff}\; 1}\lbrack s\rbrack}{2} + {\varphi_{{diff}\; 2}\lbrack s\rbrack}} \right),$

or the like.

As shown in FIG. 6, FAPC 515 may provide x′_(s) [n] and y′_(s)[n] tophase test component 520. FAPC 515 may calculate these symbols for everysub-carrier s, and for every input sample n. As further shown in FIG. 6,FAPC 515 may provide XCompValue_(s)[n] and YCompValue_(s)[n] to phaseramp component 540.

As indicated above, FIG. 6 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 6. For example, FAPC 515 may perform additional operations,fewer operations, or different operations than those described inconnection with FIG. 6.

FIG. 7 is a diagram of an example implementation 700 relating tooperations performed by phase test component (PT) 520. As describedherein in connection with FIG. 6, PT 520 may receive phase and frequencycompensated symbols x′_(s)[n] and y′_(s) [n] from FAPC 515. PT 520 mayapply test phases to each received symbol (sample), and may calculate anerror value associated with each test phase. The quantity of test phasesand the span of the test phases may be configurable. As an example,assume that PT 520 uses 8 test phases. When performing carrier recoveryfor modulation formats that have 90 degree phase symmetry, PT 520 mayuse test phases that span 90 degrees. For example, when using 8 testphases that span 90 degrees, PT 520 may evenly space the test phases byusing values of 0° (or 90°), 11.25°, 22.5°, 33.75°, 45°, 56.25°, 67.5°,and 78.75°. As another example, when using 8 test phases that span 180degrees, PT 520 may evenly space the test phases by using values of 0°(or 180°), 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, and 157.5°.

PT 520 may apply a test phase to a received sample as follows:

${x_{s}^{''}\left\lbrack {i,n} \right\rbrack} = {{x_{s}^{\prime}\lbrack n\rbrack} \times e^{{- j} \times {(\frac{i}{total})} \times {({span})}}}$${y_{s}^{''}\left\lbrack {i,n} \right\rbrack} = {{y_{s}^{\prime}\lbrack n\rbrack} \times e^{{- j} \times {(\frac{i}{total})} \times {({span})}}}$

In the above equations, x″_(s)[i,n] and y″_(s)[i,n] may represent thetest phase compensated symbols, for the n^(th) sample (or at time n) ofsub-carrier s when test phase i is applied, calculated by PT 520 for theX polarization and the Y polarization, respectively. Furthermore,x′_(s)[n] and y′_(s)[n] may represent the phase and frequencycompensated symbols received from FAPC 515, e may represent Euler'snumber, j may represent the imaginary component of the sample, i_(total)may represent the total quantity of test phases, and span may representthe span of the test phases. As an example, using 8 test phases thatspan 90 degrees, PT 520 may set span equal to π/2 radians (e.g., 90degrees), and may set i/i_(total) equal to 0/8 for the first test phase(e.g., test phase 0), to 1/8 for the second test phase (e.g., test phase1), etc., and to 7/8 for the last test phase (e.g., test phase 7, wherethe 8 test phases are identified as test phases 0 through 7). Thus,every input sample, for a particular sub-carrier and polarization, willresult in eight output samples (e.g., one for each test phase).

As further shown in FIG. 7, one or more test phase compensated symbolsfor each polarization may be provided to a decision device 710. Decisiondevice 710 may determine, for each input symbol, a symbol in theconstellation diagram with which the input symbol is most likely tocorrespond. For example, decision device 710 may use a maximumlikelihood estimation (e.g., by determining the minimum Euclideandistance between the input symbol and a symbol in the constellationdiagram). Decision device 710 may be configured based on a modulationformat of the signal (e.g., QPSK, Block-4D-BPSK, 3QAM, 16QAM, etc.).

In some implementations, decision device 710 may use two or moreconsecutive samples (e.g., n, n+1) to determine a most likely symbol(e.g., when the modulation format is Block-4D-BPSK). PT 520 may inputthe test phase compensated symbol and the most likely symbol into asubtractor 720. Subtractor 720 may determine a difference between thetest phase compensated symbol and the most likely symbol, and mayprovide the difference to a metric calculator 730.

Metric calculator 730 may calculate an error value based on thedifference. For example, metric calculator 730 may calculate a power ofthe error (e.g., a power of the difference), such as by squaring adifference of an in-phase component of the symbol (e.g., I), by squaringa difference of a quadrature component of the symbol (Q), and by summingthe squares (e.g., I²+Q²). Metric calculator 730 may calculate a firsterror value for the X polarization and a second error value for the Ypolarization. The error values calculated by metric calculator 730 forsub-carrier s and sample n using test phase i may be represented asMetricX_s[i,n] for the X polarization, and MetricY_s[i,n] for the Ypolarization.

As further shown in FIG. 7, PT 520 may provide the X and Y error valuesto an adder 740. Adder 740 may combine the X and Y error values, for aparticular sub-carrier s, test phase i, and sample n, to generate acombined error value for the particular sub-carrier s, test phase i, andsample n. The combined error value may be represented as Metric_s[i,n](e.g., which may represent a sum of MetricX_s[i,n] and MetricY_s[i,n]).By combining the X and Y error values, adder 740 may reduce noise on thecombined metric value. PT 520 may provide Metric_s[i,n] to metricfiltering component 525.

As indicated above, FIG. 7 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 7. For example, PT 520 may perform additional operations, feweroperations, or different operations than those described in connectionwith FIG. 7.

FIG. 8 is a diagram of an example implementation 800 relating tooperations performed by phase metric filtering component (MF) 525. Asdescribed herein in connection with FIG. 7, MF 525 may receive combinedmetric values (e.g., Metric_s[i,n]) from PT 520. MF 525 may averagecombined metric values across multiple sub-carriers to generate asub-carrier-averaged metric value for a particular sub-carrier s, testphase i, and sample n. Additionally, or alternatively, MF 525 mayaverage combined metric values over time to generate a time-averagedmetric value for a particular sub-carrier s, test phase i, and sample n.MF 525 may calculate the sub-carrier-averaged metric value and/or thetime-averaged metric value to reduce an amount of noise in the metricvalue.

As an example, and as shown in FIG. 8, assume that an optical channel isdivided into four subcarriers, labeled 0, 1, 2, and 3. As shown byreference number 810, assume that MF 525 receives a combined metricvalue Metric_s[i,n] for each of the four sub-carriers (e.g.,Metric_(—)0[i,n], Metric_(—)1[i,n], Metric_(—)2[i,n], andMetric_(—)3[i,n]). As shown by reference number 820, MF 525 may use anAvg_Mode indicator value to determine whether to calculate asub-carrier-averaged metric value using multiple metric values formultiple respective sub-carriers (e.g., for a particular test phase andsample). For example, if the Avg_Mode value is equal to a first value(e.g., 0), then MF 525 may not calculate a sub-carrier-averaged metricvalue.

As another example, if the Avg_Mode value is equal to a second value(e.g., 1), then MF 525 may calculate a sub-carrier-averaged metric value(e.g., SCAverage) using metric values from two different sub-carriers.For example, MF 525 may calculate SCAverage_(—)0[i, n] andSCAverage_(—)1[i,n] by averaging Metric_(—)0[i,n] and Metric_(—)1[i,n].Similarly, MF 525 may calculate SCAverage_(—)2[i,n] andSCAverage_(—)3[i,n] by averaging Metric_(—)2[i,n] and Metric_(—)3[i,n].In some implementations, MF 525 may average other combinations of metricvalues (e.g., by averaging Metric_(—)0 and Metric_(—)2, Metric_(—)0 andMetric_(—)3, etc.)

As another example, if the Avg_Mode value is equal to a third value(e.g., 2), then MF 525 may calculate the sub-carrier-averaged metricvalue using metric values from four different sub-carriers. For example,MF 525 may calculate SCAverage_(—)0[i,n], SCAverage_(—)1[i,n],SCAverage_(—)2[i,n], and SCAverage_(—)3[i,n] by averagingMetric_(—)0[i,n], Metric_(—)1[i,n], Metric_(—)2[i,n], andMetric_(—)3[i,n].

In some implementations, Avg_Mode may be a different value thandescribed above, and MF 525 may calculate the sub-carrier-averagedmetric value using metric values for different quantities (e.g., 3, 5,etc.) of sub-carriers and/or may combine metric values for differentcombinations of sub-carriers. In some implementations, the value ofAvg_Mode may be configurable (e.g., based on user input, based on amodulation format, based on a quantity of sub-carriers, etc.).

As shown by reference number 830, MF 525 may use anFFCR_Coeff[n_(start), n_(end)] value to calculate a time-averaged metricvalue (e.g., TimeAverage_s[i,n]) using multiple metric values formultiple respective samples (e.g., for a particular test phase andsub-carrier). For example, MF 525 may calculate a time-averaged metricvalue over a particular quantity of samples (e.g., from n_(start) ton_(end)). Additionally, or alternatively, MF 525 may calculate atime-weighted average (e.g., with more recent samples being weightedmore heavily than less recent samples), or may use another averagingtechnique to calculate the time-averaged metric value.

As shown by reference number 840, MF 525 may generate and provide afinal metric value, FinalMetric_s[i,n], to phase estimate component 530.In some implementations, the final metric value may be equal to thecombined metric value (e.g., Metric_s[i,n]) received from PT 520. Insome implementations, the final metric value may include asub-carrier-averaged metric value (e.g., SCAverage_s[i,n]). In someimplementations, the final metric value may include a time-averagedmetric value (e.g., TimeAverage_s[i,n]). In some implementations, thefinal metric value may include a combination of sub-carrier-averagedmetric values and time-averaged metric values. In this case, the timeaveraging and the sub-carrier averaging may be performed in any order.

As an example, MF 525 may calculate multiple sub-carrier-averaged metricvalues, for a particular sample, by averaging metric values for theparticular sample over multiple sub-carriers. MF 525 may then calculatea time-averaged metric value, for the particular sample, by averagingmultiple sub-carrier-averaged metric values over multiple samples.

As indicated above, FIG. 8 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 8. For example, MF 525 may perform additional operations, feweroperations, or different operations than those described in connectionwith FIG. 8.

FIGS. 9A and 9B are diagrams of an example implementation 900 relatingto operations performed by phase estimate component (PE) 530. Asdescribed herein in connection with FIG. 8, PE 530 may receive finalmetric values (e.g., FinalMetric_s[i,n]) from MF 525. PE 530 maydetermine a phase estimate (e.g., a most likely phase for a receivedsymbol), for a particular sub-carrier s and sample n, using all of thefinal metric values FinalMetric_s[i,n] for each test phase i.

PE 530 may calculate a phase estimate PhiEst[s,n] for a first symbol(e.g., a first received symbol) by determining a minimum final metricvalue among all final metric values for different test phases applied tothe first symbol. PE 530 may set the value of PhiEst[s,n] equal to thetest phase value associated with the minimum final metric value. Forexample, PE 530 may determine the phase estimate PhiEst[s,0] for a firstsymbol n=0, where there are 8 test phases, by calculating the following:

$\min\limits_{i:{0\rightarrow 7}}\left\{ {{FinalMetric\_ s}\;\left\lbrack {i,0} \right\rbrack} \right\}$

PE 530 may then set the value of PhiEst[s,0] equal to the phase value oftest phase i associated with the minimum final metric value. Forexample, when using 8 test phases that span 90 degrees, i={0, 1, 2, 3,4, 5, 6, 7} may correspond to test phase values of {0°, 11.25°, 22.5°,33.75°, 45°, 56.25°, 67.5°, 78.75° }. Thus, if i=2 generated the minimummetric value (e.g., FinalMetric_s[2,0]), then PE 530 may set PhiEst[s,0]equal to 22.5°.

For the second symbol (e.g., n=1), PE 530 may determine a minimum offewer than all of the final metric values for the different test phasesapplied to the second symbol. For example, to calculate PhiEst[s,1], PE530 may determine a minimum of four final metric values that centeraround PhiEst[s,0] (e.g., half of the eight total final metric valuescorresponding to the eight test phases). This avoids the issue of twominimum values discussed above in connection with FIGS. 1A and 1B. PE530 may continue to determine phase estimate values in this manner, bycalculating PhiEst[s,n+1] by determining a minimum of final metricvalues centered around PhiEst[s,n].

In some implementations, PE 530 may determine an interpolated phaseestimate value to update PhiEst[s,n]. For example, PE 530 mayinterpolate PhiEst[s,n] using a quantity of final metric values centeredaround PhiEst[s,n].

As shown in FIG. 9A, and by reference number 910, assume that PE 530receives eight final metric values associated with eight test phasevalues for a first symbol on a first sub-carrier. As shown by referencenumber 920, PE 530 may determine a minimum final metric value of fourfinal metric values associated with four consecutive test phases, suchas a minimum final metric value associated with test phase 0, 1, 2, or 3(e.g., Min[0,1,2,3]), a minimum final metric value associated with testphase 2, 3, 4, or 5 (e.g., Min[2,3,4,5]), a minimum final metric valueassociated with test phase 4, 5, 6, or 7 (e.g., Min[4,5,6,7]), and aminimum final metric value associated with test phase 6, 7, 0, or 1(e.g., Min[6,7,0,1]). Note that each of these calculations is centeredaround a different pair of test phases (e.g., 1-2, 3-4, 5-6, and 7-0).

As shown by reference number 930, once PE 530 determines a minimum finalmetric value from each group of four test phases, PE 530 may perform aninterpolation (e.g., a parabolic interpolation) to estimate aninterpolated phase value that corresponds to an actual minimum finalmetric value, as described in more detail in connection with FIG. 9B. PE530 may compare the four interpolated phase values (e.g., one from eachgroup of four test phases) to determine which one corresponds to aminimum final metric value, and may select the interpolated phase valuethat corresponds to the minimum final metric value as PhiEst[s,0]. PE530 may provide PhiEst[s,n] to phase unwrap component 535.

Additionally, or alternatively, PE 530 may calculate a group indicatorvalue (e.g., a two bit value of 0, 1, 2, or 3) to be used to select aninterpolated phase value for the next symbol (e.g., to select a valuefor PhiEst[s,1]). For example, the output of the interpolation may be asix bit value, and PE 530 may provide the four most significant bits(MSBs) to an adder that combines the four MSBs with a value of 15 toproduce a group indicator value of 0, 1, 2, or 3. When selectingPhiEst[s,n+1], PE 530 may use the group indicator value to select fromthe four interpolated phase values. For example, PE 530 may select theinterpolated phase value determined from Min[0,1,2,3] when the groupindicator value is equal to 0, may select the interpolated phase valuedetermined from Min[2,3,4,5] when the group indicator value is equal to1, may select the interpolated phase value determined from Min[4,5,6,7]when the group indicator value is equal to 2, and may select theinterpolated phase value determined from Min[6,7,0,1] when the groupindicator value is equal to 3. In this way, PE 530 may avoid the issueof selecting between two minimum values, as discussed above inconnection with FIGS. 1A and 1B.

As shown in FIG. 9B, PE 530 may perform an interpolation (e.g., aparabolic interpolation) to estimate an interpolated phase value thatcorresponds to an actual minimum final metric value. FIG. 9B shows aplot of test phases 0, 1, 2, and 3, shown as (Φ₀, Φ₁, Φ₂, and Φ₃ (e.g.,corresponding to 0°, 11.25°, 22.5°, and 33.75°, respectively), and acorresponding final metric value associated with each test phase. Thisplot may correspond to an interpolation performed after determiningMin[0,1,2,3], shown in FIG. 9A.

As shown by reference number 940, assume that test phase 1 correspondsto a minimum final metric value, as compared to test phases 0, 2, and 3.However, as shown by reference number 950, the actual minimum finalmetric value is associated with a phase value somewhere between thephase values of test phases 1 and 2 (e.g., between 11.25° and 22.5°). PE530 may use multiple test phase values and the corresponding finalmetric values to interpolate a function that relates a phase value to afinal metric value, as shown by reference number 960. As an example, PE530 may use the test phase associated with the minimum final metricvalue (e.g., Φ₁) and the two test phases on either side of that testphase (e.g., Φ₀ and Φ₂), to interpolate the function. As anotherexample, PE 530 may use all four test phase values and the correspondingfinal metric values to interpolate the function. PE 530 may use thefunction to determine an interpolated phase value that corresponds tothe minimum final metric value of the function.

As indicated above, FIGS. 9A and 9B are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 9A and 9B. For example, PE 530 may perform additionaloperations, fewer operations, or different operations than thosedescribed in connection with FIGS. 9A and 9B.

FIG. 10 is a diagram of an example implementation 1000 relating tooperations performed by phase unwrap component (PU) 535. As describedherein in connection with FIGS. 9A and 9B, PU 535 may receive a phaseestimate value PhiEst[s,n] from PE 530. The value of PhiEst[s,n] mayinclude a value between 0° and 90° for a modulation format with 90degree symmetry, a value between 0° and 180° for a modulation formatwith 180 degree symmetry, etc. However, the actual phase value of asymbol may include a value between 0° and 360°. PU 535 may convert areceived phase estimate value (e.g., PhiEst[s,n]) to an unwrapped phaseestimate value (e.g., PhiEst_(unwrap)[s,n]) between 0° and 360°.

PU 535 may determine the actual phase value by calculating a phasedifference between consecutively-received phase estimate values, such asa first phase estimate value PhiEst[s,n] and a second phase estimatevalue PhiEst[s,n+1]). PU 535 may subtract the first phase estimate valuefrom the second phase estimate value. If the result is less than a firstthreshold value, then PU 535 may add a value equal to the span of thetest phases (e.g., 90 degrees, 180 degrees, etc.) to the second phaseestimate value. If the result is greater than a second threshold value,then PU 535 may subtract a value equal to the span of the test phasesfrom the second phase estimate value. PU 535 may provide the resultingunwrapped phase estimate value PhiEst_(unwrap)[s,n] to adder 545 andfrequency estimate component 555.

As an example, and as shown in FIG. 10, assume that PhiEst[s,0], shownin FIG. 10 as Φ_(in)[0], is equal to 0°, and that PhiEst[s,1], shown inFIG. 10 as Φ_(in)[1], is equal to 85°. Assume that PU 535 determinesthat Φ_(in)[1]−Φ_(in)[0] is equal to a result of 85°, which is greaterthan a threshold value of 45° (e.g., half the distance between 0° and apositive span of 90°). Thus, PU 535 calculates PhiEst_(unwrap)[s,1],shown in FIG. 10 as Φ_(out)[1], as Φ_(in)[1]−90°=−5°.

As another example, assume that Φ_(in)[0] is equal to 90°, and thatΦ_(in)[1] is equal to 5°. Assume that PU 535 determines thatΦ_(in)[1]−Φ_(in)[0] is equal to a result of −85°, which is less than athreshold value of −45° (e.g., half the distance between 0° and anegative span of)−90°. Thus, PU 535 calculatesΦ_(out)[1]=Φ_(in)[1]+90°=95°. In this way, PU 535 may unwrap receivedphase values along a full phase cycle of 360°.

As indicated above, FIG. 10 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 10. For example, PU 535 may perform additional operations, feweroperations, or different operations than those described in connectionwith FIG. 10.

FIG. 11 is a diagram of an example implementation 1100 relating tooperations performed by adder 545, lookup table component (LUT) 550, andmultiplier 510. As described herein in connection with FIG. 10, and asshown by reference number 1110, adder 545 may receive an unwrapped phaseestimate value PhiEst_(unwrap)[s,n] from PU 535. The unwrapped phaseestimate value may be a value that combines information determined basedon the X polarization and the Y polarization. In example implementation1100, assume that CRC 460 processes 16 samples per clock cycle, and thatan optical channel that provides input to CRC 460 includes 4sub-carriers.

As shown by reference number 1120, adder 545 may also receive a phaseand frequency compensation value from FIFO Delay 540. For example, adder545 may receive a phase and frequency compensation value for the Xpolarization (e.g., XCompValue_(s)[n]) and a phase and frequencycompensation value for the Y polarization (e.g., YCompValue_(s)[n]).FIFO Delay 540 may delay providing the compensation values to adder 545to coincide with the unwrapped phase estimate value being provided toadder 545. In this way, adder 545 may properly combine the compensationvalues and the unwrapped phase estimate value (e.g., with appropriatetiming). As shown by reference number 1130, adder 545 may combine (e.g.,may sum) each phase and frequency compensation value with the phaseestimate value to determine an output phase for each polarization (e.g.,XCompValue_(s)[n]+PhiEst_(unwrap)[s,n] for the X polarization, andYCompValue_(s)[n]+PhiEst_(unwrap)[s,n] for the Y polarization). Theoutput phases may be represented using a real number.

As shown by reference number 1140, LUT 550 may receive the real numberoutput phases, and may convert the real number output phases to complexnumber output phases. For example, LUT 550 may use a lookup table toperform the conversion. As shown by reference number 1150, LUT 550 mayprovide the complex number output phases to multiplier 510. As shown byreference number 1160, multiplier 510 may also receive an input signalfrom FIFO Delay 505. For example, multiplier 510 may receive an inputsignal for the X polarization and an input signal for the Ypolarization. FIFO Delay 540 may delay providing the input signal(s) tomultiplier 510 to coincide with the complex number output phase valuebeing provided to multiplier 510. In this way, multiplier 510 mayproperly combine the input signals and the complex number output phasevalues (e.g., with appropriate timing). Multiplier 510 may combine(e.g., may multiply, rotate, etc.) each input signal value with acorresponding complex number output phase to determine acarrier-recovered output signal for each polarization.

As shown by reference number 1170, multiplier 510 may output the outputsignal (e.g., to a symbol decoder). Additionally, or alternatively, asshown by reference number 1180, multiplier 510 may provide a feedbacksignal via a feedback loop to another component of CRC 460 (e.g., PDE560). The feedback signal may be the same as the output signal, in someimplementations. In some implementations, multiplier 510 may provide thefeedback signal at a different rate than the output signal. For example,multiplier 510 may generate 16 output signals per sub-carrier per clockcycle, and may generate 2 feedback signals per sub-carrier per clockcycle, as shown.

As indicated above, FIG. 11 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 11. For example, adder 545, LUT 550, and/or multiplier 510 mayperform additional operations, fewer operations, or different operationsthan those described in connection with FIG. 11.

FIG. 12 is a diagram of an example implementation 1200 relating tooperations performed by frequency estimate component (FE) 555. Asdescribed herein in connection with FIG. 10, FE 555 may receive a set ofunwrapped phase estimate values PhiEst_(unwrap) [s,n] from PU 535. FE555 may use the set of unwrapped phase estimate values to calculate afrequency estimate value FreqEstVal (e.g., to be used by FAPC 515 tocompensate a frequency value of an input signal).

As an example, and as shown by reference number 1210, assume that FE 555receives 16 samples (e.g., per clock cycle), labeled 0 through 15, onthe first sub-carrier (e.g., s=0). As shown by reference number 1220, FE555 may calculate a difference between each pair of adjacent samples(e.g., samples n={0,1}, n={1,2}, n={2,3}, . . . n={14,15}). As shown byreference number 1230, FE 555 may sum all of these difference values tocalculate a frequency compensation error introduced by processingperformed by components 515-535.

As shown by reference number 1240, FE 555 may optionally average thefrequency compensation error across multiple sub-carriers. As shown byreference number 1250, FE 555 may be configured to include or exclude asub-carrier from the averaging operation. FE 555 may perform processingsimilar to that shown by reference numbers 1210-1230 for eachsub-carrier, and may average the frequency compensation error across twoor more sub-carriers.

As shown by reference number 1260, FE 555 may input the frequencycompensation error (or the average frequency compensation error) into adigital integrator to form a first order feedback loop to control theerror. FE 555 may control the feedback loop (e.g., an amount ofbandwidth used by the feedback loop) using a step size value. FE 555 mayoutput the frequency compensation error (or the average frequencycompensation error) to FAPC 515 as the frequency estimate valueFreqEstVal.

As indicated above, FIG. 12 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 12. For example, FE 555 may perform additional operations, feweroperations, or different operations than those described in connectionwith FIG. 12.

FIGS. 13A-13D are diagrams of an example implementation 1300 relating tooperations performed by phase difference estimate component (PDE) 560.As described herein in connection with FIG. 11, PDE 560 may receive aset of feedback signals from multiplier 510. PDE 560 may use the set offeedback signals to calculate a set of first phase difference values,phiDiff_(—)1[s], that represent a phase difference between the Xpolarization and the Y polarization for each sub-carrier s.Additionally, or alternatively, PDE 560 may use the set of feedbacksignals to calculate a set of second phase difference values,phiDiff_(—)2[s], that represent a phase difference between differentsub-carriers. As shown in FIG. 13A, PDE 560 may include a DiffPhi metricaccumulate component (DMA) 1305, a best angle estimate component (BAE)1310, a phiDiff_(—)1 update component (PhiDiff1 Update) 1315, and aphiDiff_(—)2 update component (PhiDiff2 Update) 1320.

As an example, and as shown by reference number 1325, assume that DMA1305 receives, from multiplier 510, a feedback signal on the Xpolarization and a feedback signal on the Y polarization for eachsub-carrier. Multiplier 510 may be configured to provide a particularquantity of signals per clock cycle (e.g., 2 samples per clock cycle).DMA 1305 may apply test phases to each received symbol on eachpolarization, and may calculate a metric value associated with each testphase. DMA 1305 may calculate the metric value in a similar manner as PT520, as described elsewhere herein, except that DMA 1305 may prevent themetric value for the X polarization and the metric value for the Ypolarization from being combined (e.g., DMA 1305 may perform the stepsshown by reference numbers 710-730 of FIG. 7, and may not perform thestep shown by reference number 740).

The outputs from DMA 1305 for the X polarization may be represented asphiDiffMetricX_s[i_(initial):i_(final)], where s represents asub-carrier and i_(initial):i_(final) represents each test phase fromthe first test phase i_(initial) to the last test phase i_(final).Similarly, the outputs from DMA 1305 for the Y polarization may berepresented as phiDiffMetricY_s[i_(initial):i_(final)]. As an example,and as shown by reference number 1330, when there are 8 test phases, DMA1305 may output 64 metric values, with eight for each of the twopolarizations on each of the four sub-carriers. As shown by referencenumber 1335, DMA 1305 may average each of these metric values over aparticular quantity of clock cycles (e.g., 32 clock cycles). DMA 1305may provide the metric values (or the averaged metric values) to BAE1310.

BAE 1310 may determine the test phase that results in the minimum metricvalue (e.g., a most likely test phase) for a particular polarization anda particular sub-carrier. Additionally, or alternatively, BAE 1310 mayperform an interpolation to determine a more accurate phase estimatevalue that results in a minimum metric value for the particularpolarization and the particular sub-carrier. As an example, BAE 1310 maydetermine the minimum metric value and the interpolated phase estimatevalue in a manner similar to that described elsewhere herein inconnection with PE 530.

The outputs from BAE 1310 for the X polarization (e.g., an interpolatedphase estimate value that corresponds to a minimum metric value) may berepresented as bestAngleX[s], where s represents a sub-carrier.Similarly, the outputs from BAE 1310 for the Y polarization may berepresented as bestAngleY[s]. As shown by reference number 1340, whenthere are four sub-carriers, BAE 1310 may output 8 interpolated phaseestimates, with one for each of the two polarizations and the foursub-carriers (e.g., bestAngleX[0,1,2,3] and bestAngleY[0,1,2,3]). BAE1310 may provide the interpolated phase estimate values to PhiDiff1Update 1315 and PhiDiff2 Update 1320 to update the values ofphiDiff_(—)1 [s] and phiDiff_(—)2[s], as described in more detail below.

As shown in FIG. 13B, and by reference number 1345, PhiDiff1 Update 1315may receive, for each sub-carrier, a first interpolated phase estimatevalue for the X polarization and a second interpolated phase estimatevalue for the Y polarization. As further shown, a subtractor componentmay determine a difference between the first and second interpolatedphase estimate values for a particular sub-carrier. As shown byreference number 1350, PhiDiff1 Update 1315 may input the differenceinto a digital integrator to form a first order feedback loop to drivethe difference toward zero. PhiDiff1 Update 1315 may control thefeedback loop (e.g., an update speed, a tracking speed, etc.) using astep size value. Additionally, or alternatively, PhiDiff1 Update 1315may be configured to perform the steps shown by reference numbers 1345and 1350 at a particular clock cycle interval (e.g., every 32 clockcycles, where DMA 1305 averages error values over 32 clock cycles).

The output from the integrator for sub-carrier s may be represented asphiDiff_(—)1[s], which may represent a phase difference between the Xpolarization and the Y polarization of sub-carrier s. As shown, PhiDiff1Update 1315 may provide this value to FAPC 515, which may use the valueto compensate a phase of an input signal.

As shown in FIG. 13C, and by reference number 1355, PhiDiff2 Update 1320may receive, for each sub-carrier, a first interpolated phase estimatevalue for the X polarization and a second interpolated phase estimatevalue for the Y polarization. As shown by reference number 1360,PhiDiff2 Update 1320 may determine an AvgMode indicator value, which maybe the same as the Avg_Mode indicator value discussed herein inconnection with MF 525. PhiDiff2 Update 1320 may determine a manner inwhich to update interpolated phase estimates, for a particularpolarization and across multiple sub-carriers, based on the AvgModevalue.

As an example, when AvgMode is equal to a first value (e.g., 0), theneach sub-carrier may be treated independently, and PhiDiff2 Update 1320may not update the interpolated phase estimate values. In this case,PhiDiff2 Update 1320 may set an update value for the X polarization(e.g., UpdateVecX[s]) to zero, and may set an update value for the Ypolarization (e.g., UpdateVecY[s]) to zero.

As another example, when AvgMode is equal to a second value (e.g., 1),then PhiDiff2 Update 1320 may update the interpolated phase estimatevalues by averaging across two sub-carriers. For example, when there arefour sub-carriers, PhiDiff2 Update 1320 may set two update values, for aparticular polarization, to zero as a reference value. PhiDiff2 Update1320 may set two other update values, for the particular polarization,as a difference between two interpolated phase estimate values fordifferent sub-carriers (e.g., one of the reference phase estimate valuesand another phase estimate value). For example, on the X polarization,PhiDiff2 Update 1320 may set the following update values:

-   -   UpdateVecX[0]=0    -   UpdateVecX[1]=bestAngleX[0]−bestAngleX[1]    -   UpdateVecX[2]=0    -   UpdateVecX[3]=bestAngleX[2]−bestAngleX[3]

As another example, when AvgMode is equal to a third value (e.g., 2),then PhiDiff2 Update 1320 may update the interpolated phase estimatevalues by averaging across all sub-carriers. For example, when there arefour sub-carriers, PhiDiff2 Update 1320 may set one update value, for aparticular polarization, to zero as a reference value. PhiDiff2 Update1320 may set three other update values, for the particular polarization,as a difference between a reference phase estimate value and each otherphase estimate value. For example, on the X polarization, PhiDiff2Update 1320 may set the following update values:

-   -   UpdateVecX[0]=0    -   UpdateVecX[1]=bestAngleX[0]−bestAngleX[1]    -   UpdateVecX[2]=bestAngleX[0]−bestAngleX[2]    -   UpdateVecX[3]=bestAngleX[0]−bestAngleX[3]

In some implementations, AvgMode may be a different value than describedabove, and PhiDiff2 Update 1320 may calculate the update values usingcombined interpolated phase estimate values in a different manner,and/or for a different quantity of sub-carriers.

As shown in FIG. 13D, and by reference number 1365, PhiDiff2 Update 1320may sum a first update value for the X polarization and a second updatevalue for the Y polarization on a particular sub-carrier, such as thesecond sub-carrier (e.g., s=1). As shown by reference number 1370,PhiDiff2 Update 1320 may input the summed update value into a digitalintegrator to form a first order feedback loop to drive the differencebetween the update values toward zero. PhiDiff2 Update 1320 may controlthe feedback loop using a step size value. The output from theintegrator for sub-carrier s may be represented as phiDiff_(—)2[s],which may represent a phase difference between multiple sub-carriers,and which may be used to compensate a phase of an input signal carriedby sub-carrier s. PhiDiff2 Update 1320 may provide phiDiff_(—)2[s] toFAPC 515, which may use the value to compensate the phase of the inputsignal.

As shown by reference number 1375, PhiDiff2 Update 1320 may calculatethe phase differences for the other sub-carriers in a similar manner. Asshown by reference number 1380, such a calculation may result in aphiDiff_(—)2 value of zero for a reference value.

As indicated above, FIGS. 13A-13D are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 13A-13D. For example, PDE 560 may perform additionaloperations, fewer operations, or different operations than thosedescribed in connection with FIGS. 13A-13D.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the implementations to theprecise form disclosed. Modifications and variations are possible inlight of the above disclosure or may be acquired from practice of theimplementations.

Implementations described herein reduce the computational complexity ofaccurately estimating the phase of a received symbol, and provideaccurate and efficient carrier recovery when signals are transmittedusing multiple sub-carriers, rather than a single carrier.

Some implementations are described herein in connection with thresholds.As used herein, satisfying a threshold may refer to a value beinggreater than the threshold, more than the threshold, higher than thethreshold, greater than or equal to the threshold, less than thethreshold, fewer than the threshold, lower than the threshold, less thanor equal to the threshold, equal to the threshold, etc.

It will be apparent that systems and/or methods, described herein, maybe implemented in different forms of hardware, firmware, or acombination of hardware and software. The actual specialized controlhardware or software code used to implement these systems and/or methodsis not limiting of the implementations. Thus, the operation and behaviorof the systems and/or methods were described herein without reference tothe specific software code—it being understood that software andhardware can be designed to implement the systems and/or methods basedon the description herein.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of possible implementations. In fact,many of these features may be combined in ways not specifically recitedin the claims and/or disclosed in the specification. Although eachdependent claim listed below may directly depend on only one claim, thedisclosure of possible implementations includes each dependent claim incombination with every other claim in the claim set.

No element, act, or instruction used herein should be construed ascritical or essential unless explicitly described as such. Also, as usedherein, the articles “a” and “an” are intended to include one or moreitems, and may be used interchangeably with “one or more.” Furthermore,as used herein, the term “set” is intended to include one or more items,and may be used interchangeably with “one or more.” Where only one itemis intended, the term “one” or similar language is used. Also, as usedherein, the terms “has,” “have,” “having,” or the like are intended tobe open-ended terms. Further, the phrase “based on” is intended to mean“based, at least in part, on” unless explicitly stated otherwise.

What is claimed is:
 1. An optical receiver, comprising: a digital signalprocessor configured to: receive a plurality of input signals carried bya respective plurality of sub-carriers; apply a plurality of test phasesto each input signal of the plurality of input signals; determine aplurality of error values, respectively associated with the plurality oftest phases, for each input signal of the plurality of input signals;selectively combine a first error value, of the plurality of errorvalues and associated with a first signal of the plurality of inputsignals, and a second error value, of the plurality of error values andassociated with a second signal of the plurality of input signals, thefirst signal being carried by a first sub-carrier of the plurality ofsub-carriers, the second signal being carried by a second sub-carrier ofthe plurality of sub-carriers, the second sub-carrier being differentfrom the first sub-carrier; calculate a plurality of updated metricvalues, respectively associated with the plurality of test phases, for aparticular input signal of the plurality of input signals, based onselectively combining the first error value and the second error value;compare the plurality of updated metric values associated with theparticular input signal; determine a test phase, of the plurality oftest phases, that represents an estimated phase, associated with theparticular input signal, based on comparing the plurality of updatedmetric values; determine a phase estimate value based on the test phase;and provide the phase estimate value to modify the particular inputsignal.
 2. The optical receiver of claim 1, where the digital signalprocessor, when selectively combining the first error value and thesecond error value, is further configured to: determine a mode indicatorvalue that indicates whether to combine the first error value and thesecond error value; and selectively combine the first error value andthe second error value based on the mode indicator value.
 3. The opticalreceiver of claim 1, where the digital signal processor, whenselectively combining the first error value and the second error value,is further configured to: determine a mode indicator value thatindicates whether to combine the first error value and the second errorvalue; and selectively perform a first action or a second action basedon the mode indicator value, the first action including combining thefirst error value and the second error value when the mode indicatorvalue is equal to a first value, the second action including preventingthe first error value and the second error value from being combinedwhen the mode indicator value is equal to a second value.
 4. The opticalreceiver of claim 1, where the digital signal processor, whenselectively combining the first error value and the second error value,is further configured to: determine a mode indicator value thatindicates a quantity of error values, of the plurality of error values,to be combined; and selectively perform a first action or a secondaction based on the mode indicator value, the first action includingcombining a first quantity of error values when the mode indicator valueis equal to a first value, the second action including combining asecond quantity of error values when the mode indicator value is equalto a second value, the second quantity being different from the firstquantity.
 5. The optical receiver of claim 4, where the first quantityis less than a quantity of sub-carriers included in the plurality ofsub-carriers; and where the second quantity is equal to the quantity ofsub-carriers included in the plurality of sub-carriers.
 6. The opticalreceiver of claim 1, where the digital signal processor, whendetermining the test phase, is further configured to: determine the testphase based on a minimum updated metric value of the plurality ofupdated metric values.
 7. The optical receiver of claim 6, where thedigital signal processor, when determining the phase estimate value, isfurther configured to: interpolate the phase estimate value based on theminimum updated metric value and at least one other updated metric valueincluded in the plurality of updated metric values.
 8. The opticalreceiver of claim 1, where the digital signal processor, when receivingthe plurality of input signals, is further configured to: modify aplurality of received signals to form the plurality of input signals;and receive the plurality of input signals based on modifying theplurality of received signals.
 9. A system comprising, an opticalreceiver configured to: receive a plurality of input signals carried bya respective plurality of sub-carriers; apply a plurality of test phasesto each input signal of the plurality of input signals; determine aplurality of error values, respectively associated with the plurality oftest phases, for each input signal of the plurality of input signals;calculate a plurality of updated metric values, respectively associatedwith the plurality of test phases, for a particular input signal of theplurality of input signals, based on a first error value and a seconderror value of the plurality of error values, the first error valuebeing associated with a first sub-carrier of the plurality ofsub-carriers, the second error value being associated with a secondsub-carrier of the plurality of sub-carriers, the second sub-carrierbeing different from the first sub-carrier; compare the plurality ofupdated metric values associated with the particular input signal;determine a test phase, of the plurality of test phases, that representsan estimated phase, associated with the particular input signal, basedon comparing the plurality of updated metric values; determine a phaseestimate value based on the test phase; and provide the phase estimatevalue to modify the particular input signal.
 10. The system of claim 9,where the optical receiver, when calculating the plurality of updatedmetric values, is further configured to: selectively combine the firsterror value and the second error value; and calculate the plurality ofupdated metric values based on selectively combining the first errorvalue and the second error value.
 11. The system of claim 9, where theoptical receiver, when determining the plurality of error values, isfurther configured to: determine a first metric value that represents anerror associated with a first polarization of the particular inputsignal; determine a second metric value that represents an errorassociated with a second polarization of the particular input signal,the second polarization being different from the first polarization;combine the first metric value and the second metric value; determine anerror value, of the plurality of error values and associated with theparticular input signal, based on combining the first metric value andthe second metric value.
 12. The system of claim 9, where the opticalreceiver, when comparing the plurality of updated metric values, isfurther configured to: determine a minimum updated metric value of theplurality of updated metric values; and where the optical receiver, whendetermining the test phase, is further configured to: determine the testphase associated with the minimum updated metric value.
 13. The systemof claim 9, where the optical receiver, when comparing the plurality ofupdated metric values, is further configured to: determine a minimumupdated metric value of the plurality of updated metric values; wherethe optical receiver, when determining the test phase, is furtherconfigured to: determine the test phase associated with the minimumupdated metric value; and where the optical receiver, when determiningthe phase estimate value, is further configured to: interpolate thephase estimate value based on the determined test phase and at least oneother test phase included in the plurality of test phases.
 14. Thesystem of claim 9, where the optical receiver, when comparing theplurality of updated metric values, is further configured to: identify afirst group of updated metric values included in the plurality ofupdated metric values; identify a second group of updated metric valuesincluded in the plurality of updated metric values, the second groupbeing different than the first group; determine a first minimum updatedmetric value from the first group; determine a second minimum updatedmetric value from the second group; compare the first minimum updatedmetric value and the second minimum updated metric value; select thefirst minimum updated metric value or the second minimum updated metricvalue as an overall minimum updated metric value based on comparing thefirst minimum updated metric value and the second minimum updated metricvalue; and where the optical receiver, when determining the test phase,is further configured to: determine the test phase associated with theoverall minimum updated metric value.
 15. The system of claim 14, wherethe optical receiver, when selecting the first minimum updated metricvalue or the second minimum updated metric value as the overall minimumupdated metric value, is further configured to: determine whether thefirst minimum updated metric value or the second minimum updated metricvalue has been selected; selectively set a group indicator value basedon determining whether the first minimum updated metric value or thesecond minimum updated metric value has been selected, the groupindicator value being set to a first value when the first minimumupdated metric value has been selected, the group indicator value beingset to a second value when the second minimum updated metric value hasbeen selected, the second value being different from the first value;and output the group indicator value to control whether a third minimumupdated metric value or a fourth minimum final metric value is selectedin association with determining another test phase associated withanother input signal.
 16. A method, comprising: receiving, by an opticalreceiver, a plurality of input signals carried by a respective pluralityof sub-carriers; applying, by the optical receiver, a plurality of testphases to each input signal of the plurality of input signals;determining, by the optical receiver, a plurality of error values,respectively associated with the plurality of test phases, for eachinput signal of the plurality of input signals; calculating, by theoptical receiver, a plurality of final error values, respectivelyassociated with the plurality of test phases, for a particular inputsignal of the plurality of input signals, based on a first error valueand a second error value of the plurality of error values, the firsterror value being associated with a first sub-carrier of the pluralityof sub-carriers, the second error value being associated with a secondsub-carrier of the plurality of sub-carriers, the second sub-carrierbeing different from the first sub-carrier; comparing, by the opticalreceiver, the plurality of final error values, associated with theparticular input signal, to determine a minimum final error value of theplurality of final error values; identifying, by the optical receiver, atest phase, of the plurality of test phases, associated with the minimumfinal error value; determining, by the optical receiver and based on theidentified test phase, a phase estimate value that represents anestimated phase associated with the particular input signal; andproviding, by the optical receiver, the phase estimate value to modifythe particular input signal.
 17. The method of claim 16, wherecalculating the plurality of final error values further comprises:combining the first error value and the second error value; andcalculating the plurality of final error values based on combining thefirst error value and the second error value.
 18. The method of claim16, where calculating the plurality of final error values furthercomprises: identifying a mode indicator value that indicates whether thefirst error value and the second error value are to be combined;selectively performing a first action, a second action, or a thirdaction based on the mode indicator value, the first action includingpreventing the first error value and the second error value from beingcombined when the mode indicator value is equal to a first value, thesecond action including combining a first quantity of error values,including the first error value and the second error value, when themode indicator value is equal to a second value, the second value beingdifferent from the first value, the third action including combining asecond quantity of error values, including the first error value and thesecond error value, when the mode indicator value is equal to a thirdvalue, the second quantity being different from the first quantity, thethird value being different from the first value and the second value;and calculating the plurality of final error values based on selectivelyperforming the first action, the second action, or the third action. 19.The method of claim 16, where providing the phase estimate value furthercomprises: providing the phase estimate value, via an output path, to afirst component to modify the particular input signal; and providing thephase estimate value, via a feedback path, to a second component tomodify a different input signal, the different input signal beingreceived after the particular input signal.
 20. The method of claim 16,where the plurality of input signals is a plurality of first inputsignals; where the plurality of test phases is a plurality of first testphases; where the phase estimate value is a first phase estimate value;where the particular input signal is a first particular input signal;and where the method further comprises: receiving a plurality of secondinput signals carried by the plurality of sub-carriers; applying aplurality of second test phases to each second input signal of theplurality of second input signals, a quantity of second test phasesincluded in the plurality of second test phases being fewer than aquantity of first test phases included in the plurality of first testphases; determining a second phase estimate value, that represents anestimated phase associated with a second particular input signal of theplurality of second input signals; and providing the second phaseestimate value to modify the second particular input signal.